Phosphoric acid has been used in a great amount as a raw material, for example for medicines, chemicals and semiconductors, and also in industrial fields such as automobile and electric industries for example for metal plating. It is also used in domestic detergents. Phosphoric acid contained in industrial and domestic wastewater is now causing a problem of water pollution.
On the other hand, there was estimated in the near future a global depletion of phosphorus ore by massive consumption of phosphoric acid. For that reason, there exists a need for separation and recovery of high-purity phosphoric acid from phosphoric acid-consuming industrial processes and phosphoric acid-containing wastewater.
Phosphoric acid is present as ionized in water. Accordingly, in current separation and recovery of phosphoric acid, columns packed with ion-exchange resin have been used. However, such industrial and domestic wastewater for example contains solid particles, sticky substances and water-soluble proteins alone or in combination. Thus, recovery of phosphoric acid for example from such industrial and domestic wastewater also causes similar problems. In addition, for separation and recovery of phosphoric acid contained in wastes at the industrial scale, a high-efficiency separation apparatus and a high-efficiency separation method are needed.
Continuous treatment of ion-containing water and recovery of the ions therein is carried out, as the ion-containing water is fed though a column packed with ion-exchange resin beads (see, for example, Patent Document 1). In this way, the ions are recovered as they are adsorbed on the ion-exchange resin.
However, when a processing material containing solid particles, sticky substances and water-soluble proteins alone or in combination is processed by a method of feeding the material into such a column, the column clogs easily by filtration. In particular if the processing solution contains for example water-soluble proteins, the column clogs by gelation of the proteins caused by electrostatic interaction between the water-soluble proteins and the ion-exchange resin. For that reason, there existed a problem of difficulty in continuously processing.
Accordingly, it was needed to remove the substances causing column clogging by pretreatment of the processing material. However, it caused problems such as demand for an additional step for pretreatment of the processing solution and thus an increase in cost.    Patent Document 1: Japanese Unexamined Patent Publication No. 2004-195457